[PATCH net-next v2 08/10] devlink: introduce shared devlink instance for PFs on same chip

[Jiri Pirko <jiri@resnulli.us>]

From: Jiri Pirko <jiri@nvidia.com>

Multiple PFs may reside on the same physical chip, running a single
firmware. Some of the resources and configurations may be shared among
these PFs. Currently, there is no good object to pin the configuration
knobs on.

Introduce a shared devlink instance, instantiated upon probe of
the first PF and removed during remove of the last PF. The shared
devlink instance is not backed by any device device, as there is
no PCI device related to it.

The implementation uses reference counting to manage the lifecycle:
each PF that probes calls devlink_shd_get() to get or create
the shared instance, and calls devlink_shd_put() when it removes.
The shared instance is automatically destroyed when the last PF removes.

Example:

pci/0000:08:00.0: index 0
  nested_devlink:
    auxiliary/mlx5_core.eth.0
devlink_index/1: index 1
  nested_devlink:
    pci/0000:08:00.0
    pci/0000:08:00.1
auxiliary/mlx5_core.eth.0: index 2
pci/0000:08:00.1: index 3
  nested_devlink:
    auxiliary/mlx5_core.eth.1
auxiliary/mlx5_core.eth.1: index 4

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
---
v1->v2:
- s/err_kstrdup_id/err_devlink_free/
- fixed kernel-doc comment of devlink_shd_get()
- removed NULL arg check in devlink_shd_get/put()
---
 include/net/devlink.h |   6 ++
 net/devlink/Makefile  |   2 +-
 net/devlink/sh_dev.c  | 142 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 149 insertions(+), 1 deletion(-)
 create mode 100644 net/devlink/sh_dev.c

diff --git a/include/net/devlink.h b/include/net/devlink.h
index 45dec7067a8e..e97ee09af5d6 100644
--- a/include/net/devlink.h
+++ b/include/net/devlink.h
@@ -1647,6 +1647,12 @@ void devlink_register(struct devlink *devlink);
 void devlink_unregister(struct devlink *devlink);
 void devlink_free(struct devlink *devlink);
 
+struct devlink *devlink_shd_get(const char *id,
+				const struct devlink_ops *ops,
+				size_t priv_size);
+void devlink_shd_put(struct devlink *devlink);
+void *devlink_shd_get_priv(struct devlink *devlink);
+
 /**
  * struct devlink_port_ops - Port operations
  * @port_split: Callback used to split the port into multiple ones.
diff --git a/net/devlink/Makefile b/net/devlink/Makefile
index 000da622116a..8f2adb5e5836 100644
--- a/net/devlink/Makefile
+++ b/net/devlink/Makefile
@@ -1,4 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0
 
 obj-y := core.o netlink.o netlink_gen.o dev.o port.o sb.o dpipe.o \
-	 resource.o param.o region.o health.o trap.o rate.o linecard.o
+	 resource.o param.o region.o health.o trap.o rate.o linecard.o sh_dev.o
diff --git a/net/devlink/sh_dev.c b/net/devlink/sh_dev.c
new file mode 100644
index 000000000000..f4da25e8f8bc
--- /dev/null
+++ b/net/devlink/sh_dev.c
@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Copyright (c) 2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
+
+#include <net/devlink.h>
+
+#include "devl_internal.h"
+
+static LIST_HEAD(shd_list);
+static DEFINE_MUTEX(shd_mutex); /* Protects shd_list and shd->list */
+
+/* This structure represents a shared devlink instance,
+ * there is one created per identifier (e.g., serial number).
+ */
+struct devlink_shd {
+	struct list_head list; /* Node in shd list */
+	const char *id; /* Identifier string (e.g., serial number) */
+	refcount_t refcount; /* Reference count */
+	char priv[] __aligned(NETDEV_ALIGN); /* Driver private data */
+};
+
+static struct devlink_shd *devlink_shd_lookup(const char *id)
+{
+	struct devlink_shd *shd;
+
+	list_for_each_entry(shd, &shd_list, list) {
+		if (!strcmp(shd->id, id))
+			return shd;
+	}
+
+	return NULL;
+}
+
+static struct devlink_shd *devlink_shd_create(const char *id,
+					      const struct devlink_ops *ops,
+					      size_t priv_size)
+{
+	struct devlink_shd *shd;
+	struct devlink *devlink;
+
+	devlink = devlink_alloc(ops, sizeof(struct devlink_shd) + priv_size,
+				NULL);
+	if (!devlink)
+		return NULL;
+	shd = devlink_priv(devlink);
+
+	shd->id = kstrdup(id, GFP_KERNEL);
+	if (!shd->id)
+		goto err_devlink_free;
+	refcount_set(&shd->refcount, 1);
+
+	devl_lock(devlink);
+	devl_register(devlink);
+	devl_unlock(devlink);
+
+	list_add_tail(&shd->list, &shd_list);
+
+	return shd;
+
+err_devlink_free:
+	devlink_free(devlink);
+	return NULL;
+}
+
+static void devlink_shd_destroy(struct devlink_shd *shd)
+{
+	struct devlink *devlink = priv_to_devlink(shd);
+
+	list_del(&shd->list);
+	devl_lock(devlink);
+	devl_unregister(devlink);
+	devl_unlock(devlink);
+	kfree(shd->id);
+	devlink_free(devlink);
+}
+
+/**
+ * devlink_shd_get - Get or create a shared devlink instance
+ * @id: Identifier string (e.g., serial number) for the shared instance
+ * @ops: Devlink operations structure
+ * @priv_size: Size of private data structure
+ *
+ * Get an existing shared devlink instance identified by @id, or create
+ * a new one if it doesn't exist. Return the devlink instance with a
+ * reference held. The caller must call devlink_shd_put() when done.
+ *
+ * Return: Pointer to the shared devlink instance on success,
+ *         NULL on failure
+ */
+struct devlink *devlink_shd_get(const char *id,
+				const struct devlink_ops *ops,
+				size_t priv_size)
+{
+	struct devlink_shd *shd;
+
+	mutex_lock(&shd_mutex);
+
+	shd = devlink_shd_lookup(id);
+	if (!shd)
+		shd = devlink_shd_create(id, ops, priv_size);
+	else
+		refcount_inc(&shd->refcount);
+
+	mutex_unlock(&shd_mutex);
+	return shd ? priv_to_devlink(shd) : NULL;
+}
+EXPORT_SYMBOL_GPL(devlink_shd_get);
+
+/**
+ * devlink_shd_put - Release a reference on a shared devlink instance
+ * @devlink: Shared devlink instance
+ *
+ * Release a reference on a shared devlink instance obtained via
+ * devlink_shd_get().
+ */
+void devlink_shd_put(struct devlink *devlink)
+{
+	struct devlink_shd *shd;
+
+	mutex_lock(&shd_mutex);
+	shd = devlink_priv(devlink);
+	if (refcount_dec_and_test(&shd->refcount))
+		devlink_shd_destroy(shd);
+	mutex_unlock(&shd_mutex);
+}
+EXPORT_SYMBOL_GPL(devlink_shd_put);
+
+/**
+ * devlink_shd_get_priv - Get private data from shared devlink instance
+ * @devlink: Devlink instance
+ *
+ * Returns a pointer to the driver's private data structure within
+ * the shared devlink instance.
+ *
+ * Return: Pointer to private data
+ */
+void *devlink_shd_get_priv(struct devlink *devlink)
+{
+	struct devlink_shd *shd = devlink_priv(devlink);
+
+	return shd->priv;
+}
+EXPORT_SYMBOL_GPL(devlink_shd_get_priv);
-- 
2.51.1